U.S. manufacturing is back. That’s been the conventional economic wisdom now for several months, and there’s plenty of proof to back it up – rising factory output, strong manufacturing production gains, and lower labor costs that make American workers more attractive. Couple that with the natural gas boom underway in the U.S., which many experts believe will lower energy costs for U.S. manufacturers, and you’ve got a resurgence of a sector that has been shrinking as a percentage of the economy for several decades. “We are probably the most competitive, on a global basis, than we’ve been in the past 30 years,” says GE CEO Jeff Immelt. “Will U.S. manufacturing go from 9% to 30% of all jobs? That’s unlikely. But could you see a steady increase in jobs, over the next quarters and years. I think that will happen.”

But at least one economic seer, Goldman Sachs’ chief economist Jan Hatzius, is throwing a bit of cold water on the idea. He recently released a report, which is getting a lot of attention on the web, arguing that the U.S. “manufacturing renaissance” is cyclical, not structural – meaning, the sector is doing as well as would have been predicted under any circumstances at this point in an economic recovery, and that the gains don’t point to a real seismic shift in U.S. manufacturing competitiveness. “Measured productivity growth has been strong,” admits Hatzius in the report, entitled “U.S. Manufacturing Renaissance: Fact or Fiction?” “But U.S. export performance – arguably a more reliable indicator of competitiveness—remains middling at best.”

It’s a very interesting point, and it matters a lot to the broader economy. Nations that do better in manufacturing gain an edge in the global economy: For every $1 of manufacturing output in a community, there’s another $1.48 of wealth created. That’s why economic advisors to the President, like National Economic Council head Gene Sperling, have been pushing pro-manufacturing policies. But the Goldman report would seem to indicate that the strength in U.S. manufacturing output reflects more the relative weakness of Europe (which is mired in a debt crisis) and Japan, rather than a long-term positive shift in the U.S. itself. “Over the next few years, the manufacturing sector should continue to grow a bit faster than the overall economy,” notes the report. “But the main reason is likely to be a broad improvement in aggregate demand rather than a structural U.S. manufacturing renaissance.”

Hatzius was on holiday this week and unavailable for comment (we’ll be following up with him next week), but one immediate question is whether exports really do provide a more accurate picture, as the report suggests. It may be that more goods manufactured in the U.S. are staying in the U.S. As we’ve traveled around the country reporting on this topic over the last couple of years, a number of big industrial firms have pointed to growing demand for their products here at home – Caterpillar, which makes an increasing amount of its large earth-moving equipment for domestic mining, agriculture, and energy operations, is a great case in point.

Then there’s the question of how to look at the productivity numbers. While U.S. productivity is up over the last several years relative to, say, China, which has been flat (and also suffers from rising wages), the big question is how much more it can go up. We feel there’s reason to be bullish on the growth potential there, given how materials science and the evolution of the “industrial internet” are fundamentally reshaping manufacturing in the U.S.’s favor. The once separate steps of designing a product, making or buying the parts, and then putting everything together are beginning to blend — a consequence of technologies such as additive manufacturing and 3-D printing. It means that manufacturing wants to be closer to engineering and design — a dynamic that would likely benefit the U.S., which still rules those high-end job categories. Add the ability to include sensors in every part and process, and you’ve got a whole new manufacturing ecosystem that allows companies to accelerate product development cycles and deliver more variety and value more quickly to ever more fickle consumers.

Of course, the jobs that are being created aren’t your father’s (or grandfather’s) factory jobs of knocking in four bolts a minute for eight hours a day. The new economics of Made in the USA are built in large part around acquiring cutting-edge technologies ahead of global competitors and then using those new techniques to produce more efficiently on super-automated factory floors. And while all the technology will translate into higher end jobs, it will also mean — barring dramatic growth — fewer jobs overall, especially in the middle. Positions will either be high end, or lower paid, since workers still have to compete with cheaper overseas labor (even with wage inflation in China, it will be years before the Chinese are on par with U.S. wages). It’s no accident that many of the new manufacturing clusters in the U.S. are in the South, where unions hold less power. “Yes, manufacturing is coming back, but it’s evolving into a very different type of animal than the one most people recognize today,” says James Manyika, says James Manyika, director of McKinsey Global Institute, which recently did an exhaustive study on this shift entitled “Manufacturing the Future.” “We’re going to see new jobs, but no where near the number some people expect, especially in the short term.”

It’s a sentiment that stands in sobering contrast to President Obama’s second term goal of creating a million new manufacturing jobs in four years. Some of the difference may lie in semantics. As Manyika points out, labor statistics underestimate the reality of manufacturing, since they count mainly jobs inside factories. Related positions in, say, Ford’s marketing department, or small businesses doing industrial design or creating new software for big exporters don’t get tallied. Yet these jobs wouldn’t exist but for the big factories. The official 9% of U.S. employment represented by manufacturing belies the importance of the sector to our overall economy. Manufacturing represents a whopping 67% of all private sector R & D spending, as well as 30% of the country’s productivity growth.

In short, manufacturing’s value can be measured in many different ways. “The ability to make things is fundamental to the ability to innovate things over the long term,” says Willy Shih of Harvard Business School and co-author of Producing Prosperity: Why America Needs a Manufacturing Renaissance. “When you give up making products you lose a lot of the added value.” That’s as good a reason as any to care about the future of manufacturing.